An urn contains $w$ white and $b$ black balls. $n$ extractions without replacement are made. What are the probabilty of:
- get a black ball on $i-th$ extraction?
- get a black ball on $i-th$ extraction and white on $j-th$ extraction, with $j > i$?
I know that the hypergeometric distribution doesn't care about position, so what is the math behind this problem?